Among the various video display systems available in the art, an optical projection system is known to be capable of providing high quality images in a large scale.
In FIG. 1, there is illustrated a prior art optical projection system 100 comprising non-point white light source 1, a Schlieren bar 2 provided with a plurality of reflective surfaces and corresponding number of slits, a source lens 3, a projection lens 4, a field lens system 5, a projection screen 6, a beam splitting means 7 including a first and a second dichroic mirrors 8, 9, and first, second and third arrays 10, 11, 12 of M.times.N actuated mirrors 13.
In such a system, a white light emanating from the non-point white light source 1 is focussed along a first optical light path onto the reflective surfaces of the Schlieren bar 2 by the source lens 3, wherein the white light consists of a first, a second and a third primary light beams, each of the primary light beams being one of the primary colors. The reflective surfaces of the Schlieren bar 2 are in a facing relationship with the source lens 3 and the field lens system 5. The white light reflected from each of the reflective surfaces diverges along a second optical path and is collimated by the field lens system 5, thereby being uniformly illuminated onto the beam splitting means 7 including the first and second dichroic mirrors 8,9, wherein the first dichroic mirror 8 is disposed between the field lens system 5 and the second dichroic mirror 9 facing the first array 10 of M.times.N actuated mirrors 13, and the second dichroic mirror 9, between the first dichroic mirror 8 and the third array 12 of M.times.N actuated mirrors 13 facing the second array 11 of M.times.N actuated mirrors 13. The first dichroic mirror 8 receives the white light from the field lens system 5, reflects the first primary light beam of the white light to the first array 10 of M.times.N actuated mirrors 13, and transmits the second and third primary light beams to the second dichroic mirror 9, which, in turn, receives the second and third primary light beams from the first dichroic mirror 8, reflects the second primary light beam to the second array 11 of M.times.N actuated mirrors 13, and transmits the third primary light beam to the third array 12 of M.times.N actuated mirrors 13. Each of the actuated mirrors 13 of the arrays 10, 11, 12 corresponds to each of the pixels to be displayed.
The optical path of the reflected primary light beams from each of the actuated mirrors 13 in each of the arrays 10, 11, 12 is determined by the amount of deflection thereof.
The reflected primary light beams from each of the undeflected actuated mirrors in each of the arrays 10, 11, 12 are focussed back to the Schlieren bar 2 by the field lens system 5 via the first and second dichroic mirrors 8, 9 along the second optical path and stopped by the reflective surfaces thereof, whereas the reflected primary light beams from each of the deflected actuated mirrors in each of the arrays 10, 11, 12 are focussed back to the Schlieren bar 2 by the field lens system 5 via the first and second dichroic mirrors 8, 9 along a third optical path so that a portion of the focussed light beams passes the slits thereof. The primary light beams from each of the actuated mirrors 13 in each of the arrays 10, 11, 12 which pass through the slits are transmitted to the projection lens 4 which projects the transmitted primary light beams from each of the actuated mirrors 13 in each of the arrays 10, 11, 12 on the projection screen 6, thereby displaying each of the pixels corresponding thereto.
One of the major shortcomings of the above-described optical projection system 100 arises from the use of the Schlieren bar 2. Since the white light emanating from the non-point light source 1 is focussed onto the reflective surfaces of the Schlieren bar 2 at a fixed angle, the reflected white light therefrom is extremely divergent and has a large beam diameter, and in order to uniformly illuminate such a white light onto the beam splitting means 7 and onto the arrays 10, 11, 12 of M.times.N actuated mirrors 13 and then refocus the reflected light from the arrays 10, 11, 12 of M.times.N actuated mirrors 13 to the Schlieren bar 2, the field lens system 5 employed therein must become extremely complicated.